The present invention relates to a treated fiber and a method of forming a treated fiber. Such treated fibers find many applications, for example, in nonwoven fabrics, yarns, carpets, and otherwise where fibers having one or more modified properties are desired.
Nonwoven fabrics are finding increasing use in various applications, including personal care absorbent articles such as diapers, training pants, incontinence garments, mattress pads, wipers, and feminine care products (e.g., sanitary napkins), medical applications such as surgical drapes, gowns, wound care dressings, and facemasks, articles of clothing or portions thereof including industrial workwear and lab coats, household and industrial operations including liquid and air filtration, and the like.
It is often desirable to modify the properties of the nonwoven fabric to perform a function or meet a requirement for a particular application. One means of modifying the properties is through the use of treatments. Treatments are generally added by either topically treating the fibers or fiber web or by mixing the treatment with the polymer prior to forming fibers by melt extrusion or the like. Examples of typical types of treatments include, but are not limited to, stabilizers, delusterants, flame retardants, fillers, antimicrobial agents, optical brighteners, extenders, colorants, lubricants, antistatic agents, alcohol repellents, softeners, soil repellents, wetting agents, processing aids, and other functional chemistries.
Once an appropriate treatment is identified for an application, the means of applying the treatment to the fiber or fiber web often presents challenges. Some treatments may be applied either internally or topically, depending on the chemical structure of the treatment and any process limitations.
Topical treatment, or coating, of a formed fiber or fiber web may be accomplished by various techniques, including foam treating as disclosed in U.S. Pat. No. 4,095,558 (Ellegast et al.), roll coating as disclosed in U.S. Pat. No. 3,993,805 (Roberts), spray coating as disclosed in U.S. Pat. No. 3,032,813 (Stalego), slot coating as disclosed in U.S. Pat. No. 4,457,034 (Simmen) and U.S. Pat. No. 5,679,158 (Holzer, Jr. et al.), brush treating as disclosed in European Patent No. 0 594 983 A1 (Garavaglia et al.), and dip and squeeze treating, which consists of submerging the fiber in a treatment bath followed by blotting or squeezing to remove the excess, as disclosed in U.S. Pat. No. 5,151,321 (Reeves et al.). When only a low level of treatment is required, such systems may result in poor treatment uniformity on the fiber or fiber web surface. As a result, it is often necessary to increase the treatment level or dilute the treatment to form a treatment bath. The treatment process may then be followed by a costly and/or cumbersome drying step that may adversely impact the physical properties, such as strength, of the fiber or fiber web. Further, the application of multiple immiscible treatments may require a multi-step coating and drying process.
Traditionally, internal treatment has been achieved by compounding a treatment into a polymer and blending the compounded product with untreated polymer pellets prior to extrusion as disclosed in U.S. Pat. No. 4,167,503 (Cipriani), or by directly combining the treatment with the molten polymer during extrusion as disclosed in U.S. Pat. Nos. 4,857,251 and 5,057,262 (Nohr et al.). Such processes require extensive mixing to attain uniformity of the treatment in the fiber and lengthy purge times to remove the treatment from the extruder during typical manufacturing process changes.
An alternative approach, exemplified by U.S. Pat. No. 5,516,476 (Haggard et al.), blends the treatment with the molten polymer by passage through mixer channels in the spin pack plates immediately upstream of the spinning orifices of a spinneret. This approach shortens the purge time but does not use all treatments efficiently, as many treatments are functional only on the fiber surface and provide little or no benefit when in the interior of the fiber. Treatments that are not miscible with the polymer may migrate to the fiber surface over time, but even highly migratory treatments may not diffuse to the surface completely. As a result, higher treatment levels are often required to achieve the desired fiber properties. As with the topical treatment systems, internal treatment systems may be limited to use of a single treatment or blends of miscible treatments, since the incorporation of multiple immiscible treatments may result in fiber formation difficulties and poor treatment uniformity on the surface of the fiber.
Thus, traditional topical treatment systems are limited in terms of uniformity, cost, and flexibility, but are useful for applying the treatment only to the surface of a fiber or fiber web where its functional benefit is often desired. Internal treatment systems may simplify the treatment process, but are often inefficient due to long polymer purge times or increased treatment level requirements to obtain the desired properties on the surface of the fiber. Thus, a system that offers the benefits of both topical treatment and internal treatment is highly desirable.
The prior art has not presented a method nor an apparatus for selectively applying one or more treatments to the surface of an advancing molten polymer without mixing with the polymer. Such a process would allow for rapid product changes, highly efficient use of treatment and polymer, the use of multiple immiscible treatments, minimal drying requirements, if any, and reduced processing interruptions.
The present invention provides a treated fiber and a method of forming a treated fiber. A molten polymer is delivered to a fiber spinning assembly adapted to form and distribute a polymer stream. At least one treatment is applied in a liquid state to at least one region on the surface of the molten polymer stream within the fiber spinning assembly. A substantial portion of the treatment remains on the surface of the formed fiber within the region to which the treatment was applied.
Any polymer that is suitable for a fiber formation process may be used to form a treated fiber of the present invention. Similarly, any type of treatment may be used, for example, wetting agents, skin care treatments, medicinal treatments, and antistatic agents, provided that the treatment is able to withstand the processing conditions used during fiber formation processes and does not adversely impact fiber formation. The level of treatment may range from about 0.05% to about 3.0% by weight of the fiber, for example, and preferably ranges from about 0.1% to about 1.5% by weight of the fiber. The treatment is preferably a liquid or in a form which can be transported in a liquid carrier, i.e, in a liquid state.
In one embodiment, one or more regions on the surface of the molten polymer are treated with a single treatment or blend of multiple treatments. The region may be circumferential, i.e., in a direction around the fiber, or longitudinal, i.e., in a direction along the length of the fiber. The region may be continuous or discontinuous. The degree of coverage may vary from little coverage to complete coverage of the fiber surface, depending on the requirements for the particular application.
In another embodiment, two or more treatments are applied to multiple regions on the surface of the fiber. The regions may be in contact with one another or may be separate and distinct. The treatments may be miscible or immiscible.
In still another embodiment, a nonwoven web is produced with selectively treated fiber regions. This is accomplished through design of one or multiple fiber spinning assemblies to treat selected fibers or to apply multiple treatments. The regions of the fibers in the nonwoven web may vary in treatment type, amount, or degree of coverage.
The method of forming a treated fiber and the treated fiber of the present invention can be used to make nonwoven fabrics for a variety of applications. The broad scope of the applicability of the present invention will become apparent to those of skill in the art from the details given hereafter. However, it should be understood that the detailed description of the preferred embodiments of the present invention is given only by way of illustration because various changes and modifications well within the spirit and scope of the invention should become apparent to those of skill in the art in view of the following detailed description.